1. Field of the Invention
The present invention relates generally to television receivers and, more particularly, is directed to a television receiver of the so-called picture-in-picture type in which a sub-picture screen is displayed within a main picture screen in a picture-in-picture fashion.
2. Description of the Prior Art
In the prior art, there is known a television receiver of a so-called picture-in-picture type in which a sub-picture screen is displayed within a main picture screen in an inset fashion.
As will be described later, the picture-in-picture type television receiver is provided with a memory to reproduce a picture on a sub-picture screen. When the writing of a video signal into the memory and the reading of the same video signal out of the memory are alternately carried out continuously, a real moving picture can be displayed on the sub-picture screen.
According to the prior art picture-in-picture type television receiver, the following signal sources for the main picture displayed on the main picture screen and the sub-picture displayed on the sub-picture screen are employed: a high frequency signal from, for example, a television broadcast, a CATV and the like, and an external, base band video signal from an apparatus such as a VTR (video tape recorder), a video disc and so on.
With respect to television broadcasts, it often happens that two interesting programs, such as a baseball program from a certain broadcast station and a golf program from other broadcast station, are broadcast simultaneously. In such a case, some prior art picture-in-picture type television receivers can not utilize effectively the sub-picture function to reproduce the two separate programs on the main and sub-picture screens. So, it is desired that the picture-in-picture type television receiver can receive and simultaneously display the high frequency signals of two systems.
However, when the picture-in-picture type television receiver is provided with two tuners for that purpose, if channel selection keys from "0" to "9" (ten keys), an up key and a down key for incrementing and decrementing the channel number are provided for each tuner, the keys become too numerous, causing useless confusion and misoperation by the user and so on.
In addition, since the television receiver and a remote controller for it are restricted in the area in which the operation keys used for various kinds of control operations can be mounted, it is difficult to increase the number of operation keys.
The switch between the television broadcast receiving mode (TV mode) and the external video signal reproducing mode (video mode) must be done within the picture-in-picture type television receiver. If the mode switching and the channel selection by the tuner are associated, this makes the circuit arrangement thereof complicated. In the prior art receivers of this type, the mode switching and the channel selection are carried out independently.
However, if the mode switching keys and the channel selection operation mechanism are separately provided for the main picture and the sub-picture tuners, the number of keys is increased even more, thus making the above mentioned defects more serious.